20,996 research outputs found
Genomic function during the lampbrush chromosome stage of amphibian oogenesis
Throughout its lengthy developmental history the disposition of the genetic material in the amphibian oocyte nucleus differs from that in other cell types. The chromosomes in the oocyte nucleus, arrested for the whole of oogenesis at the prophase of the first meiotic division, are known to contain at least the tetraploid amount of DNA.(1,2) Oogenesis in amphibia requires months or even years to complete, depending on the species
CF6-6D engine short-term performance deterioration
Studies conducted as part of the NASA-Lewis CF6 jet engine diagnostics program are summarized. An 82-engine sample of DC-10-10 aircraft engine checkout data that were gathered to define the extent and magnitude of CF6-6D short term performance deterioration were analyzed. These data are substantiated by the performance testing and analytical teardown of CF6-6D short term deterioration engine serial number (ESN) 451507
CF6-6D engine performance deterioration
Cruise cockpit recordings and test cell performance data in conjunction with hardware inspection data from airline overhaul shops were analyzed to define the extent and magnitude of performance deterioration of the General Electric CF6-6D model engine. These studies successfully isolated short-term deterioration from the longer term, and defined areas where a significant reduction in aircraft energy requirements for the 1980's can be realized. Unrestored losses which remain after engine refurbishment represent over 70% of the loss at engine shop visit. Sixty-three percent of the unrestored losses are cost-effective to restore which could reduce fuel consumed by CF6-6D engines in 1980 by 10.9 million gallons
1966 Beef Cattle Progress Report of Research Activities
Many beef cattle breeders in the United States and other countries are following the progress of the selection experiment at the Fort Robinson Beef Cattle Research Station, Crawford, Nebraska. Three lines of Hereford cattle from the same genetic foundation are under selection. Line 21 is selected for 200-day weight. Line 22 is selected for yearling weight. Line 23 is selected for an index combining yearling weight and a score for muscling and fat thickness.
Each line is operated as a closed herd so it will be possible to determine how much improvement in economic traits can be made by selecting all replacement stock from within the same herd. Starting in 1966 there will be 150 calving cows in each line. Six herd sires are used each year. Two bulls and 25 heifers are selected to add to each line each year. Heifers are bred to calve first as two year olds. Cow numbers will be maintained at 150 by culling the oldest cows and those that fail to conceive or have a major physical unsoundness. Bulls are replaced after their third breeding season
Beef Cattle Progress Report
Efficiency of sugar beet farming can be improved by feeding beet top silage to livestock.
In two recent trials at the Scotts Bluff Experiment Station lambs fed unwilted beet top silage as the only roughage gained significantly faster than lambs fed corn silage.
Amounts of concentrates were comparable (Nebraska Experiment Station Quarterly, Fall, 1962).
This experiment compared the feeding value of a complete mixture of unwilted beet tops and concentrate added at the time of ensiling, with beet top silage and concentrate handled separately. A conventional corn silage and concentrate ration was used as a control.
Results showed that a complete ration prepared by mixing unwilted beet tops and concentrates at the time of ensiling did not produce greater gains than a ration of unwilted beet top silage and concentrates fed separately
Jamming under tension in polymer crazes
Molecular dynamics simulations are used to study a unique expanded jammed
state. Tension transforms many glassy polymers from a dense glass to a network
of fibrils and voids called a craze. Entanglements between polymers and
interchain friction jam the system after a fixed increase in volume. As in
dense jammed systems, the distribution of forces is exponential, but they are
tensile rather than compressive. The broad distribution of forces has important
implications for fibril breakdown and the ultimate strength of crazes.Comment: 4 pages, 4 figure
Mixed Symmetry Solutions of Generalized Three-Particle Bargmann-Wigner Equations in the Strong-Coupling Limit
Starting from a nonlinear isospinor-spinor field equation, generalized
three-particle Bargmann-Wigner equations are derived. In the strong-coupling
limit, a special class of spin 1/2 bound-states are calculated. These solutions
which are antisymmetric with respect to all indices, have mixed symmetries in
isospin-superspin space and in spin orbit space. As a consequence of this mixed
symmetry, we get three solution manifolds. In appendix \ref{b}, table 2, these
solution manifolds are interpreted as the three generations of leptons and
quarks. This interpretation will be justified in a forthcoming paper.Comment: 17 page
A Quasi-Spherical Gravitational Wave Solution in Kaluza-Klein Theory
An exact solution of the source-free Kaluza-Klein field equations is
presented. It is a 5D generalization of the Robinson-Trautman quasi-spherical
gravitational wave with a cosmological constant. The properties of the 5D
solution are briefly described.Comment: 10 pages Latex, Revtex, submitted to GR
The Formation of the Double Pulsar PSR J0737-3039A/B
Recent timing observations of the double pulsar J0737-3039A/B have shown that
its transverse velocity is extremely low, only 10 km/s, and nearly in the Plane
of the Galaxy. With this new information, we rigorously re-examine the history
and formation of this system, determining estimates of the pre-supernova
companion mass, supernova kick and misalignment angle between the pre- and
post-supernova orbital planes. We find that the progenitor to the recently
formed `B' pulsar was probably less than 2 MSun, lending credence to
suggestions that this object may not have formed in a normal supernova
involving the collapse of an iron core. At the same time, the supernova kick
was likely non-zero. A comparison to the history of the double-neutron-star
binary B1534+12 suggests a range of possible parameters for the progenitors of
these systems, which should be taken into account in future binary population
syntheses and in predictions of the rate and spatial distribution of short
gamma-ray burst events.Comment: To appear in MNRAS Letters. Title typo fix only; no change to pape
Tunneling out of a time-dependent well
Solutions to explicit time-dependent problems in quantum mechanics are rare.
In fact, all known solutions are coupled to specific properties of the
Hamiltonian and may be divided into two categories: One class consists of
time-dependent Hamiltonians which are not higher than quadratic in the position
operator, like i.e the driven harmonic oscillator with time-dependent
frequency. The second class is related to the existence of additional
invariants in the Hamiltonian, which can be used to map the solution of the
time-dependent problem to that of a related time-independent one.
In this article we discuss and develop analytic methods for solving
time-dependent tunneling problems, which cannot be addressed by using quadratic
Hamiltonians. Specifically, we give an analytic solution to the problem of
tunneling from an attractive time-dependent potential which is embedded in a
long-range repulsive potential.
Recent progress in atomic physics makes it possible to observe experimentally
time-dependent phenomena and record the probability distribution over a long
range of time. Of special interest is the observation of macroscopical
quantum-tunneling phenomena in Bose-Einstein condensates with time-dependent
trapping potentials. We apply our model to such a case in the last section.Comment: 11 pages, 3 figure
- …